The present invention relates generally to a semiconductor device, and more particularly to a semiconductor device in which semiconductor element or elements are housed in a package including a heat sink.
FIG. 4 is a partially cutaway perspective view illustrating a conventional semiconductor device. The semiconductor device shown in FIG. 4 comprises a heat sink 41, and a semiconductor element 42 such as an integrated circuit device and the like mounted on the surface of the heat sink 41. The semiconductor device of FIG. 4 further comprises a sidewall 43 which is attached to the surface of the heat sink 41 and which surrounds the semiconductor element 42, and a cap not shown in the drawing which closes the opening portion of the sidewall 43 and covers the semiconductor element 42. In other words, the semiconductor element 42 is housed within a container having the heat sink 41, the sidewall 43 and the cap.
In the sidewall 43, a plurality of leads 44 are provided such that the leads 44 are partially buried in the sidewall 43 and penetrate the sidewall 43. One end of each of the leads 44 is coupled with a coupling pad 46 of the semiconductor element 42 via a bonding wire 45 and the like.
Fixing of the semiconductor element 42 to the heat sink 41, fixing of the sidewall 43 to the heat sink 41 and fixing of the cap to the sidewall 43 are respectively done by using thermosetting resin.
Japanese patent laid-open publication No. 11-238838 discloses another conventional semiconductor device. The semiconductor device disclosed in this publication has a similar structure to that of the semiconductor device shown in FIG. 4, except for the following. That is, the heat sink has projections at the peripheral portion thereof and the projections fit into concave portions formed in the sidewall, or the frame shaped sidewall is fit inside the projections formed in the heat sink. Thereby, an influence of the thermal expansion can be suppressed and disconnection of the bonding wires can be avoided.
According to the recent development in mobile communications, the size of a semiconductor device for use in a transmitter has become larger and larger, and an output power thereof has become higher and higher. Therefore, heat generation of such semiconductor device has become larger and larger. As a result, it is required that the package of the semiconductor device has far superior heat dissipating performance.
However, the conventional semiconductor devices mentioned above have a problem that, because of an increase in the size thereof and an increase in thermal expansion caused by an increase in heat generation, there arises a warp in the heat sink. Even in the semiconductor device disclosed in the Japanese patent laid-open publication No. 11-238838 in which thermal expansion of the frame member is suppressed by the heat sink, this problem arises when the size of such semiconductor device becomes large.
Also, the conventional semiconductor devices have a problem that, according to an increase in the size thereof and an increase in the thermal expansion caused by an increase in heat generation, an adhesive which joins the sidewall to the heat sink can not withstand the stress caused by the difference of thermal expansion between the sidewall and the heat sink, and junction between the sidewall and the heat sink becomes broken. Especially, this disjunction often occurs between the heat sink and the adhesive, because of the materials of the heat sink and the adhesive.
In the semiconductor device disclosed in the Japanese patent laid-open publication No. 11-238838 in which thermal expansion of the frame member is suppressed by the heat sink, gas which is produced when the adhesive is thermally cured and which causes voids can not escape effectively. Therefore, airtightness of the semiconductor package is deteriorated.
Therefore, it is an object of the present invention to provide a semiconductor device in which a warp in a heat sink does not occur even when a temperature of the semiconductor device has changed largely and thereby a high heat dissipating efficiency can be realized.
It is another object of the present invention to provide a semiconductor device in which junction between a heat sink and a sidewall of a semiconductor package is not broken even when a temperature of the semiconductor device has changed largely and thereby high airtightness can be maintained.
It is still another object of the present invention to provide a semiconductor device which has high reliability and uniform quality.
It is still another object of the present invention to obviate the disadvantages of the conventional semiconductor device having a heat sink.
According to an aspect of the present invention, there is provided a semiconductor device comprising: a heat sink on which a semiconductor element is mounted; a sidewall which is attached onto the heat sink and which surrounds the semiconductor element; wherein one of the heat sink and the sidewall has a plurality of projections formed on a joining surface thereof to be joined to an opposing surface of the other one of the heat sink and the sidewall; wherein a gap is formed by the projections between the sidewall and the heat sink when the sidewall is disposed on the heat sink; and wherein the sidewall and the heat sink are joined together by using low elasticity liquid resin which fills at least the gap formed by the projections between the sidewall and the heat sink.
In this case, it is preferable that the projections are formed on the heat sink.
It is also preferable that each of the projections have a height of 200 xcexcm or larger.
It is further preferable that the low elasticity liquid resin is thermosetting epoxy resin, and the sidewall and the heat sink are joined by thermally curing the low elasticity liquid resin.
It is advantageous that the modulus of elasticity of the low elasticity liquid resin becomes 1000 kgf/mm2 or smaller after thermally curing the low elasticity liquid resin.
According to another aspect of the present invention, there is procided a method of manufacturing a semiconductor device having a heat sink on which a semiconductor element is mounted and a sidewall which is attached onto the heat sink and which surrounds the semiconductor element, the method comprising: forming a plurality of projections on a joining surface of one of the heat sink and the sidewall, the joining surface is a surface to be joined to an opposing surface of the other one of the heat sink and the sidewall; disposing the sidewall on the heat sink; filling a gap formed by the projections between the heat sink and the sidewall with low elasticity liquid resin; and joining the heat sink and the sidewall by curing the low elasticity liquid resin.
In this case, it is preferable that the low elasticity liquid resin is cured in the condition the sidewall is pressed onto the heat sink.
It is also preferable that the projections are formed on the heat sink.
It is further preferable that the low elasticity liquid resin is thermosetting epoxy resin, and the sidewall and the heat sink are joined by thermally curing the low elasticity liquid resin.
It is advantageous that the modulus of elasticity of the low elasticity liquid resin becomes 1000 kgf/mm2 or smaller after thermally curing the low elasticity liquid resin.